Public Health Significance of Urban Pests
Allergic asthma
21 20
combination of exposure and sensitization to cockroach allergens is a stronger risk fac- tor for asthma morbidity in the inner cities of the United States than is exposure and sen-
sitization to allergens produced by dust mites, cats or dogs Gruchalla et al., 2005.
1.4. Rodents and asthma 1.4.1. Sensitization and symptoms
Most of what is known about allergic reactions to mice and rats originates from occupa- tional studies. Symptoms of allergy, including rhinitis, conjunctivitis and asthma, have
been reported by workers in animal laboratories, notably those that work with rats and mice Taylor, Longbottom Pepys, 1977; Renstrom et al., 1994; Hollander et al., 1997;
Lieutier-Colas et al., 2002. In the 1970s, British researchers reported that five people who worked with laboratory animals developed asthma within two weeks to two years of star-
ting to work with mice and rats Taylor, Longbottom Pepys, 1977. Within a year of developing asthma, all five workers experienced asthma symptoms after only a few minu-
tes of exposure to the animals. These studies were among the first to show that urinary proteins from rats and mice, rather than fur, elicited stronger positive skin prick tests and
bronchial hyperreactivity. In a multi-site study of 650 people who worked in animal labo- ratories in the Netherlands, Sweden and the United Kingdom, researchers found that
9.7 of the workers were sensitized to rat urinary allergens Heederik et al., 1999. They also found a higher risk of sensitization to rats associated with high exposure to rat aller-
gens.
Recently, researchers realized that mouse and rat allergens might also contribute to the development or exacerbation or both of childhood allergic asthma. Polish researchers
found that 61 of inner-city children exposed to detectable levels of mouse allergen were skin prick positive to these allergens, whereas only 14 of children with levels below the
limit of detection were sensitized to mice Stelmach et al., 2002a. In 2000, a study of 499 children in the United States with asthma found that 18 were allergic to mouse aller-
gen and that those with exposure to Mus m 1 an allergen in mouse urine 1.6 µgg in kitchen dust were more likely OR = 2.2 to become sensitized to the mouse allergen than
those with a lower level of exposure Phipatanakul et al., 2000a. Among the same cohort of children, allergy to rats was also prevalent 21, and those with sensitization and
exposure to rat allergens experienced more unscheduled medical visits, hospitalizations and days with diminished activity due to asthma Perry et al., 2003. While the terms
urban
and suburban are somewhat subjective, it is of interest to report that mouse aller- gens measured in suburban homes in the United States have also been associated with
sensitization to mouse allergen, as judged by a skin prick test Phipatanakul et al., 2005. Specifically, quartile increases in bed dust Mus m 1 median: 0.76 µgg; interquartile
range: 0.16–3.20 µgg were associated with a greater likelihood of having a positive skin prick test OR = 1.4. This finding suggests that even low levels of mouse allergen can
pose a risk of developing allergic sensitization. Furthermore, Polish researchers found that children of workers in animal laboratories were also allergic to mice and rats, sug-
gesting that passive transfer of rodent allergens from work to the home might be a bio- logically relevant exposure pathway Krakowiak, Szulc Gorski, 1999.
1.4.2. Exposure
1.4.2.1. Size characteristics of airborne mouse and rat allergens
Occupational studies are the source of most of the size characterization of particles that bear rodent allergens. Dutch researchers conducted ambient and personal air sampling
in seven laboratory animal facilities and found that rat and mouse allergens were contai- ned mainly on particles larger than 5.8 µm in aerodynamic diameter Hollander et al.,
1998. In a French study of 12 rat breeding facilities, different tasks resulted in varying levels of exposure to allergens Lieutier-Colas et al., 2001. Rat n 1 is an allergen from
rats, and changing cages and feeding the rats were associated with an average level of 91.1 ng Rat n 1 per m3 of air compared with an average level of 0.4 ng Rat n 1 per m3
of air for office duties. Both the Dutch and French researchers found that the greater the number of animals in a room, the higher the allergen level. In the United Sates, 13 rooms
of a major animal handling facility were sampled for airborne mouse allergen Mus m 1, and the particles were size fractionated Ohman et al., 1994. Among the rooms without
mice, most of the Mus m1 was contained on 0.4–10-µm-diameter particles. However, most of the Mus m 1 in rooms with a high density of mice was found on particles lar-
ger than 10 µm in aerodynamic diameter.
1.4.2.2. Residential exposures
Mouse allergens have been measured in dust and, to some extent, air samples from homes in urban and suburban environments where children reside. In some studies, Mus m 1
was measured with a monoclonal antibody ELISA; in others, mouse urinary proteins MUP, which include Mus m 1, were measured with polyclonal antibody-based ELISAs
Phipatanakul et al., 2000a; Chew et al., 2003; Cohn et al., 2004, but the two allergen measurements were highly correlated r = 0.96, P 0.001 Chew et al., 2003. Mus m 1
levels in bed dust were as high as 294 µgg, with a median level of 0.5 µgg in a multi-site study of asthmatic children living in inner cities across the United States Phipatanakul
et al., 2000a. In a national survey of American homes urban, suburban and rural, the median MUP level in bed dust was 0.25 µgg Cohn et al., 2004. The median MUP level
was 0.5 µgg for bed dust in low-income New York City homes Chew et al., 2003, which was slightly higher than that median = 0.23 µgg for Polish inner city homes Stelmach
et al., 2002a. Mouse allergen levels have been found to be consistently higher in kitchen dust than in bed dust. The level of mouse allergen in the air of homes where children
reside is usually lower than that in occupational settings; however, the levels can be rela- tively high Chew, Correa Perzanowski, 2005; Matsui et al., 2005. While one study
observed that mouse allergen levels were lower among cat owners, all studies found asso- ciations between problems reported by residents with rodents and increased levels of
mouse allergens. Reasons for differences in home characteristics being predictive of mouse allergen levels are explained in greater detail in section 1.2.1.
Unlike mouse allergens, rat allergens in house dust have not been associated positively with sensitization Perry et al., 2003; Phipatanakul et al., 2005. The reason for this disparity
could be that significant rat allergen exposure might also occur outside of the home, such as in subways, schools and restaurants, and that home measurement of this allergen might
Public Health Significance of Urban Pests
Allergic asthma
23 22
not be representative of total exposure. Although the same could be said for mouse aller- gen, it appears that a significant exposure to mouse allergen does arise from homes.
Nevertheless, high levels of mouse allergen ≥ 2 µgg were found in 78 of New York City school classrooms during at least one sampling season Chew, Correa Perzanowski,
2005 and ranged from 0.3 µgg to 118µgg in 12 urban Baltimore schools Amr et al., 2003.
1.5. Dust mites and asthma 1.5.1.Sensitization and asthma
